The present invention relates to a catalyst composition for homopolymerization or copolymerization of olefins.
Ziegler-Natta catalysis for the polymerization of olefins is a widely known catalytic process. A typical Ziegler-Natta catalyst comprises a transition metal compound and a cocatalyst. The transition metal compound may be supported on a support. Supports suitable in A Ziegler-Natta catalysis are known from the prior art to be common refractory oxide supports, such as silica. However, polymeric supports have been developed in recent years. A number of patents claim the use of polymers as supports for polymerization catalysts. U.S. Pat. No. 4,900,706 discloses that polymer supports may be impregnated with titanium, magnesium and chlorine as a component for a catalyst for olefin polymerization wherein copolymers of olefins and styrene are the preferred polymer supports. U.S. Pat. No. 5,118,648 discloses the use of porous polymer supports, with the preferred embodiment comprising divinyl benzene cross-linked polystyrene.
Further, U.S. Pat. No. 5,412,070 discloses that terpolymers of ethylene, propylene and carbon monoxide (aliphatic polyketone) may be effectively employed as a support for a palladium-based catalyst system. In U.S. Pat. No. 5,952,456 it is similarly suggested to use polyketone as a support for the preparation of aliphatic polyketones, but specifically it is disclosed that when an aluminoxane is used it may be attractive to employ commercially available supported aluminoxane, for example methyl aluminoxane on silica.
Anyone skilled in the art is aware of the broad range of electron donors, including ethers, used in association with Ziegler-Natta-catalysts. Consequently, the widest possible chemical resistance available is advantageous in selecting a polymer support material. Polymeric supports also have the advantage of short, low temperature drying steps and reportedly higher tolerance to water and oxygen impurities compared to traditionally used refractory oxide supported catalysts.
However, the polymer supports disclosed in the prior art typically suffer some weaknesses that decrease their utility in this particular application. Compared to oxide supported catalysts the polymer supports known are much more expensive.
It is therefore an object of the present invention to provide a catalyst composition for polymerization of olefins comprising a polymer support which overcomes the drawbacks of the prior art.
Further, it is an object of the present invention to provide a process for homopolymerization or copolymerization of olefins wherein such a catalyst composition may be utilized.
The object regarding the catalyst composition is solved by a catalyst composition for homopolymerization or copolymerization of olefins comprising:
(a) a solid catalyst precursor comprising a transition metal compound of group IVB, VB, or VIB of the periodic table, a magnesium compound and aliphatic polyketone particles; and
(b) a cocatalyst comprising an aluminum alkyl, an aluminoxane or mixtures thereof.
Surprisingly, it was found that aliphatic polyketone may be excellently used as a polymeric support in the field of Ziegler-Natta-catalysis. Aliphatic polyketone has a high melting point, good chemical resistance and mechanical strength.
Further, it is non-friable, insensitive to common solvents and tolerant to typical catalyst components. In preparation of such an aliphatic polyketone support the dehydration step is relatively short and may be carried out at comparatively lower temperatures.
The high melting point, chemical resistance and strength of aliphatic polyketones offer the opportunity to realistically compete with silica as a support. Typical aliphatic polyketones melt at over 210xc2x0 C. with a high level of ductility and resistance to common organic solvents.
Aliphatic polyketones allow for reaction of the polymer with reducing agents and presumably with Grignard reagents to afford a low-chlorine, magnesiumalkoxide supported catalyst. Therefore, one further advantage is the lack of chlorine in the aliphatie polyketone.
With regard to the reaction of aliphatic polyketones with reducing agents these aliphatic polyketones have to be differentiated from the widely know aromatic polyketones. Typicial aromatic polyketones have virtually inaccessible ketone sites, which make them very poor candidates for a reaction with Grignard reagents. The bulk of the polymer backbone of the aromatic polyketones makes them unlikely candidates for surface modification. Further, aromatic polyketones generally have very high melting temperatures.
The use of aliphatic polyketone as a support in the catalyst composition according to the present invention has the following advantages:
reduced chlorine content relative to traditional chlorinated supported catalysts, such as polyvinylchloride;
low potential toxicity;
an electron donor is xe2x80x9cbuilt inxe2x80x9d in an unreacted, accessible ketone site;
high solvent resistance;
reactivity of aliphatic ketone sites to reducing and alkylating agents (such as hydrates, aluminum alkyls and Grignard reagents);
secondary and tertiary alkoxides which have been claimed to enhance activity, bulk density, etc. may be xe2x80x9cbuilt inxe2x80x9d from the support;
high temperature resistance of aliphatic polyketones that can allow for higher preparation temperatures;
good aluminum alkyl compatibility;
higher chemical and thermal stability during processing relative to xe2x80x9cstandard polymersxe2x80x9d.
In summary, using aliphatic polyketone as a support for the catalyst composition of the present invention offers a unique blend of the properties of silica and polymer supports known in the prior art.
Preferably, the polymer particles of the aliphatic polyketone have a mean particle diameter of about 5 to about 10,000 xcexcm, preferably about 15 to 500 xcexcm, a pore volume of at least about 0.1 cm3/g, a pore diameter of at least about 500 to 10,000 Angstrom and a surface area of from about 0.2 m2/g to about 50 m2/g, and are, most preferably, regularly shaped.
Aliphatic polyketone suitable as a support for the catalyst composition of the present invention may have a molecular weight in the range of about 3,000 to about 300,000 g/mole.
The polymer particles used in the present invention have labile aliphatic ketone groups as surface active sites. Preferably, these active sites are reacted stoichiometrically with the organo-metallic compound.
Aliphatic polyketone particles offer significant advantages over traditional olefin polymerization catalysts using supports such as silica or magnesium chloride. In contrast to the silica supported catalyst, the polymer particles described in the present invention require substantially milder conditions for dehydration. Their chemical resistance to solvents is unique among most other polymer supports. The stability of the aliphatic polyketone polymer adds significant flexibility to catalyst preparation conditions in terms of solvents and temperature. The polyketone polymer used in the present invention is also commercially available at a significant cost savings compared to silica or magnesium chloride supports. Besides the lower cost of the polymer, the catalyst benefits from very low metal loadings, both of which decrease the final catalyst cost and diminish the ash in the final product. Also, the catalyst in the present invention is more active than conventional silica or magnesium chloride supported Ziegler-Natta catalysts and some supported metallocene catalysts.
Further, the catalyst composition of the present invention may comprise an electron donor which may be oxygenated organic material, such as diethers, diesters, alkyl carbonates and the like, or aryl or alkyl chlorides, such as monochlorbenzene, or mixtures thereof. The most preferred electron donor is ethylbenzoate
The transition metal compound may be represented by the general formula M(OR1)nX4-n wherein M represents a transition metal of group IVB, VB or VIB of the periodic table, R1 represents an alkyl group, aryl group or cycloalkyl group having 1 to 20 carbon atoms, X represents a halogen atom and 0xe2x89xa6nxe2x89xa64.
Non-limiting examples of the transition metal are titanium, vanadium, or zirconium, examples of R1 include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl and the like.
Preferable examples of the above-mentioned transition metal compounds include the following: titaniumtetrachloride, methoxytitaniumtrichloride, dimethoxytitaniumdichloride, ethoxytitaniumtrichloride, diethoxytitaniumdichloride, propoxytitaniumtrichloride, dipropoxytitaniumdichloride, butoxytitaniumtrichloride, dibutoxytitaniumdichloride, vanadiumtrichloride, vandiumtetrachloride, vanadiumoxytrichloride and zirconiumtetrachloride.
The magnesium compound used in the catalyst composition of the present invention may be represented by the general formula R2MgX, wherein R2 is an alkyl group having 1 to 20 carbon atoms, and X is a halogen atom, preferably chlorine. Other preferable magnesium compounds are represented by the general formula R3R4 Mg, wherein R3 and R4 are different or the same alkyl groups having 1 to 20 carbon atoms.
Preferable examples of the above-mentioned magnesium compounds include the following: dialkylmagnesium, such as diethylmagnesium, dipropylmagnesium, di-iso-propylmagnesium, di-n-butylmagnesium, di-iso-butylmagnesium, butylethylmagnesium, dihexylmagnesium, dioctylmagnesium, butyloctylmagnesium, alkylmagnesium chloride, such as ethylmagnesium chloride, butylmagnesium chloride, hexylmagnesium chloride or mixtures thereof.
Activators for the titanium sites may be represented by the general formula R6nAlX3-n or R7 R8xe2x80x94Alxe2x80x94Oxe2x80x94AlR92, wherein R6, R7, R8 and R9 each represent a hydrocarbon group having 1 to 10 carbon atoms; X represents a halogen atom or an alkoxy group and 0=n=3. Illustrative but not limiting examples include trialkylaluminums such as trimethylaluminum, triethylaluminum, triisobutylaluminium, tri-n-hexylaluminum; dialkylaluminum chloride such as dimethylaluminum chloride, diethylaluminum chloride; alkylaluminum dichlorides such as methylaluminum dichloride, ethylaluminum dichloride; dialkylaluminum methoxide such as dimethylaluminum methoxide, diethylaluminum ethoxide, or mixtures thereof. The preferred activators for the titanium sites are trimethylaluminum, triethylaluminum, triisobutylaluminum and tri-n-hexylaluminum.
The organoaluminum compound or organoaluminum compounds in this invention may be used in the range of about 1 to 1500 moles of aluminum per one mole of transition metal in said catalyst composition, and more preferably in the range of about 50 to 800 moles of organoaluminum compound per one mole of transition metal.
The gel permeation chromatography of the polymers produced by the catalyst composition of the invention shows typical Ziegler-Natta profiles. Activities are in the range of 1 to 9 kg polymer per gram catalyst per hour under typical Ziegler-Natta conditions.
The polymers prepared by the use of the catalyst composition reported in the invention are linear homopolymers of olefins such as ethylene, or copolymers of ethylene with one or more C3-C10 alpha-olefins. Particular examples of these copolymers include ethylene/propylene copolymers, ethylene/1-butene copolymers, ethylene/1-pentene copolymers, ethylene/1-hexene copolymers, ethylene/heptene copolymers, ethylene/1-octene copolymers, ethylene/4-methyl-1-pentene copolymers. Ethylene/1-hexene and ethylene/1-butene are the most preferred copolymers polymerized with the use the catalyst composition of the present invention.
According to one embodiment, a copolymer of ethylene and carbon monoxide is used as polymeric support. The preparation of the solid catalyst component in the present invention involves drying the polymer at a low temperature under reduced pressure for a relatively short period. The polymer is then suspended in an organic solvent. Nonlimiting examples of solvents include alkanes or ethers. The polymeric material is then treated with a magnesium compound described above at a temperature in the range of about xe2x88x9210xc2x0 to 200xc2x0 C. The amount of magnesium compound to polymer support can be in the range of 0.1 mmol to 10 mmol per gram polymer. Chemcial modification of the surface of the polymer can also be used to enhance the aliphatic polyketone""s properties as a support. For example, as disclosed in U.S. Pat. No. 5,955,562 aliphatic polyketones can be precisely reduced on the surface to hydroxyl groups and then subsequently reacted with a silane. The bulk properties of the polymer are claimed to be retained.
The resulting supported catalyst product is then suspended in such organic solvents including alkanes such as hexane, cyclohexane, heptane, isooctane and pentamethylheptane, or ethers such as ethylether or methyltertiarybutylether. The product material is then treated with a transition metal compound described above at a temperature in the range of about 0xc2x0 to 120xc2x0 C. Typical metal halides include titanium tetrachloride, vanadium tetrachloride and zirconium tetrachloride. The product is then washed with a suitable solvent such as isopentane, hexane, cyclohexane, heptane, isooctane and pentamethylheptane, preferably isopentane or hexane. The produced solid catalyst component is then washed with a suitable solvent such isopentane, hexane, cyclohexane, heptane, isooctane and pentamethylheptane, preferably isopentane or hexane, and then dried using a nitrogen purge at a temperature in the range of about 20xc2x0 C. to 80xc2x0 C.
The final solid catalyst component has a loading of about 0.05-8% titanium by weight. The thus-formed catalyst component is activated with suitable activators, also known as cocatalysts, for olefins polymerization. The preferred compounds for activation of the solid catalyst component are organoaluminum compounds.
Further advantages and features of the present invention will now be described in detail by way of example. The following examples are intended to be illustrative of this invention. They are, of course, not to be taken in any way limiting on the scope of this invention. Anyone skilled in the art could envision derivations of this technology too numerous to mention.